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Sill, W. R.

Publications and source records attributed to Sill, W. R..

12 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Orbital radar evidence for lunar subsurface layering in Maria Serenitatis and Crisium

Data from the lunar-orbiting Apollo 17 radar sounding experiment (60-m wavelength) have been examined in both digital and holographic formats, and it is concluded that there are two subsurface radar reflectors below the surface in Mare Serenitatis and one reflector below the surface in Mare Crisium. The mean apparent depths of the reflectors below the surface of the former Mare are 0.9 and 1.6 km, while the reflector below the surface of the latter Mare has a mean depth of 1.4 km. These reflectors represent basin-wide subsurface interfaces. Techniques for reducing surface backscatter (clutter) in the data are described, and reasons for thinking that the distinct alignments in radar returns represent subsurface reflecting horizons are explained

Peeples, W. J.↗
NASA NTRS1972

Interaction of the solar wind with a planetary ionosphere

An electrodynamic model for an ionosphere-solar wind interaction is developed based on the existence of a low beta plasma below the anemopause. The currents for the interaction are driven by the solar wind motional electric field and induce a stagnation magnetic field at the anemopause. For Venus and Mars the lower region of the ionosphere near the electron density peak has the highest conductivity, and therefore the tangential component of the induction current flows substantially in this region. The current paths close in the anemopause, which is a solar wind current sheath analogous to the magnetopause. Both the fraction of the undisturbed solar wind motional electric field, which drives the induction current, and the required fraction of incident solar wind particles, crossing the anemopause to produce this current, are shown to be small.

Blank, J. L.↗
NASA NTRS1971

Lunar conductivity models from the Apollo 12 magnetometer experiment

A number of conductivity models were investigated for compatibility with Apollo 12 magnetometer data. Except at the highest frequencies, a simple core-crust model is compatible with the observed dayside transfer function, which is expressed as the ratio of the lunar surface field spectrum to the interplanetary magnetic field spectrum. All conductivity profiles exhibit a peak near 1500 km, when the models are constrained to conform to the observed flat response at the higher frequencies. However, at frequencies above .01 Hz the long wavelength limitation of the theoretical model is no longer valid. A plausible explanation for the difference between the north-south and east-west transfer functions is that it is due to a time-varying compression of the remanent (dc) field at the Apollo 12 site by fluctuations in the solar wind plasma.

Sill, W. R.↗